Artificial fibroin thread



PatentedFe b. 1 2 1935 I UNITED STATE -,In,order to obtain a silk threadfromithisgvis- 1 ARTIFICIAL FIBROIN THREAD Heinrich Fink, Premnitz, and Ernst 'Rossnery Rathenow, Germany, assignorsto I. G. Farbenind'ustrie Aktiengesellschaft, Frankfort-onthe-Main, Germany c No Drawing. Application N vember, 12, '1929,

Serial No. 406,718. In Germany November 14,

, Our'present invention relatesfto a new proc-j ess of manufacturing in' a continuous manner long, practically endless, fine threads from the.

wastes of natural silk by dissolvingethem and subsequently reprecipitating them in. a coagulating bath.

Another object'of our invention is to provide a solution of natural silk waste in which the fibroin molecule is practically not decomposed and from which fine threads are. obtainable. which are equivalent to cultivated natural silk fibers. Additional objects of our invention are the newthreads, further objects of our invention relating, ,for instance, to the precipitating bath and to the method, ofspinning, will be seen from the detailed specification following hereafter. The whole crux of our invention-can well be exemplifiedby brief discussion of. the prior art. Efforts have been made'to dissolve natural silk in organic acids or in hydrochloric acid. By spinning, however, threads from thesesolutions, hard andbrittle products were obtained. The fibroin -molecule is decomposed by these sclventspso that sult. r

Considerablybetter results were obtained by these methods did not lead to a satisfactory'redissolving silk at a raised'ftemperature in neutral, strongly water soluble salts and by drawing out the viscous mass inthreads whenthe precoagulation is complete. Spinning on'a factory scale according to the said-process is, however, scarcely, possible, because the pre coagulation .requires'a very long time, viz. A; hour and more,

and a difficultly perceptible coagulation optimum lies within narrow ranges. Furthermore, the solutions easily separate f into their component parts, whereby an extremely viscous mass isproduced; in spite of exact observation of the 1'8 quired spinning conditions, often threads of infe'rior quality cr no threads atall are obtained.

By our present invention; all these disadvantages are remedied; one may dissolve natural silk wastes at ordinary temperature with the formation of a viscous mass which is stable for a sufiiciently long time and which canbe spun without difficulties.

- We have found that ortho-phosphoric acid "is.

very well suited as a solvent for naturalsilk. L A

I solution of wastes of silk in phosphoric acid prepared at room temperature is stable forseveral hours even at ordinary temperature; at 090. its

ability of being regenerated is not affected for one day and even more. a

cous solution, we use a precipitating bath con- 7 ocl ims. (Class'18- -54y V taining an aqueous solution of alkali metal salts of strong, acids, for instance 'a 'halogenacid, sulfuric acid, phosphoric acid, nitric acid, preferably in the presence of alkali metal salts of weak tionin two stages by theaction of two isups.-.

quent precipitating baths from which the first hasa weaker precipitating action on the fibroin solution than the second. The'firstbath preferably consists in the main of a concentrated so1u-' tion 'of"an'alkali metal'salt of a mineral acid.

The best'result'is'not obtained if a sodiumsalt or' a" 'p'otassium salt is individually used, but rather when'a mixture of potassium and sodium s PATENT oFFIcE salts is used. To'enhance the coagulating veloc-. V

ity of the precipitating bath a saturated aqueous solution of alkaliformate or acetate is added to it? in a quantity corresponding-to k, to fig of its" volume. Furthermore, formaldehyde may be'added composition permits one to' spinwithout difiiculty even when the thread tobe formed is imfmersed' in 1the1first bath in a length of only 10' to 20 cm: 1 r

Afterhaving' passed the first bath the thread formedis guided immediately in a second bath consisting inthemain of a saturated solution of an alkali'metal salt'of formic acid, acetic acid or other iatty acids, or of a mixture cf these salts. We may add a salt of an aliphatic hydroxy acid or an aliphatic acid containing a carbonyl group, for instance. lactic acid or pyro-racemic' acid." A salt of lactic: acid, for instance; prevents recrystallization of thesalts contained inthe pre-..

cipitating solution on'the threads after having left the'bath.'- Because of this, said salts may likewise be added to the firstprecipitatingbath.

Evens'after having passedthe second precipi-: tating .bath, the thread is still water-soluble or at least 'swellable in .water. It becomes waterinsoluble' after having run-alonger spaceg in 'the air,,and. after. :having been stretchedfives to eightfoldof .its originallength. '[I henit may be collected on a spool, freed from salt andacid by washing and soaping.

V a" v the salt solution forming "the first precipitating bath to improve the tenacity of the thread and to increase the spinning velocity. Abath of this When spinning threads of our'fibroin solution through a nozzle provided with a plurality of fine holes, it may occur that the individual fibers stick together. To avoid this disadvantage, we add to the acid fibroin solution a small quantity of an ethereal oil, for instance, turpentine. 0.02 to 0.1 per cent of oil calculated on the quantity of the fibroin solution are suflicient. By addition of the oil the fibroin solution is colored weakly brown, this coloration, however, has no influence on the finished thread. This addition hascertain advantages. The individual threads are set free more easily on the spinning nozzle and the I capacity of being spun and the uniformity'o'i the threads is enhanced. Furthermore, as men-. tioned above, the single threads do not stick together and are separated from each other completely by an after-treatment with wetting agents or soap. I v The following example serves to illustrate our invention: 7

1 part of natural silk wastes is dissolved while stirring or kneading in 10 parts of phosphoric acid 'of 85 per cent strength. Then 0.04 per cent of turpentine, calculated on the quantity of the solution, are added. The viscous, weakly yellowish-brown solution is filtered and freed from air bubbles I by centrifuging. This solution is pressed from acooled storing vessel 'with or without the use of a spinning pump in the first precipitating bath through a glass nozzle provided for instance with 120 holes of 0.08 mm. diameter. This first precipitating bath contains per liter Grams Sodium chloride 132 Potassium chloride 122 Sodium lactate 21 Potassium lactate .25 Sodium formats. 22 Potassium formate 28 Anhydrous formaldehyde 15 This precipitating solution thus contains I V Grams Hydrochloric acid 142 Lactic acid 34 Formic acid 30 bound by about equal parts of potassium and The length of immersion of-the thread may be varied between 10 to 800m. -The bath is kept at room temperature- After having passed the first bath, the thread is guided, suitably over an easily movable roll, in the second bath consisting of a saturated aqueous solution of ammonium formate to which $4; of its volume of a concentrated sodium lactate solution has been added. The temperature of this second bath is also room temperature. The length of immersion in this bath. is chosen as long .as possible, preferably longer than 50 cm. After having left this bath, the thread runs through a space of air of about one or more meters. The drawing speed is so regulated that the thread is. at most weakly stretched on its way from the spinning nozzle through the precipitating baths and through the air space. Only after having passed the air space, is'the thread stretched; by means of a stretching device, fiveto eightfold of its original length by guiding it, for instance, over a plurality of rolls rotating with increased circumferential speed.-'Then it is collected on a spool, washed, soaped-anddricd. I

In this manner, soft and lustrous threads with an individual titer of one denier and with a dry tenacity up to 2 grams per denier and a wet tenacity more than 1 gram per denier and of an extensibility of. about 12 per cent are obtainable.

Our threads show no decomposition of fibroin, they yield all chemical reactions of the genuine fibroin 'of natural silk and have the same optical behavior in'polarizcd light as natural silk. The X-ray diagram of our threads is not different from that of natural silk. They differ, however, from natural silk bybeing digested by proteases.

Various modifications and changes in details of the conditions given in the foregoing example are considered to be within the spirit of the invention and the scope of the following claims. The composition of the precipitating baths may be varied within certain limits. As mentioned above, ammonium "salts are equivalents of the alkali metal salts and may substitute them in the coagulating liquids. The first precipitating bath may be used for a long time, even after it has dissolved an essential quantity of phosphoric acid.

What we claim is:

l. The process of manufacturing artificial fibroin threads which comprises dissolving nat ural silk in phosphoric acid, causing the viscous solution to pass through suitably formed openings to come into contact with a precipitating liquid, and imparting a stretch to the pre-coagulated thread after it leaves the coagulating bath.

2. The process of manufacturing artificial fibroin threads which comprises dissolving natural silk in phosphoric acid, causing the viscous solution to pass through suitably formed openings to come into contact with a liquid comprising a concentrated aqueous solution'of an alkali metal salt of a strong mineral acid; and imparting a stretch to the pre-coagulated thread after it leaves the coagulating bath.

3. The process of manufacturing artificial fibroin threads which comprises dissolving natural silk in phosphoric acid, adding an ethereal oil, causing the viscous solution to pass through suitably formed openings to come into contact with a liquid comprising a concentrated aqueous solution of an alkali metal salt of a strong mineral acid, and imparting a stretch to the precoagulated thread after it leaves the coagulating bath. v

4. The process of. manufacturing artificial fibroin threads which comprises dissolving natural silk in phosphoric acid, adding an ethereal oil, causing the'viscous solution to pass through suitably formed openings to come into contact with a liquid comprising a concentrated aqueous solution of analkali metal salt of a strong mineral acid, passing the thread through a second liquid comprising a concentrated aqueous solution of an alkali metal salt of a lower fatty acid, and imparting a stretch to the thread after it leaves the second precipitating bath.

5.; The process of manufacturing artificial fibroin threads which comprises dissolving natural silk in phosphoric acid, adding an ethereal oil, causing the viscous solution to pass through suitably formed openings to come into contact with a liquid comprising a concentrated solution of a potassium and a sodium saltof a strong mineral acid and containing'formaldehyde, passing the thread through a second liquid comprising a concentrated aqueous solution of analkali metal-salt-of alower fatty acid, and imparting Iggy Z 88 ural silk in phosphoric acid, adding an ethereal oil, causing the viscous solution to pass through suitably formed openings to come into contact with a liquidcomprising a concentrated solution of a potassium and a sodium salt of a strong mineral acid and containing formaldehyde and an alkali metal salt of an aliphatic acid of the group consisting of hydroxy acids and'acids containing the carbonyl group, passing the thread through a second liquid comprising a concentrated aqueous solution of an alkali 'metal salt of a lower fatty acid, and imparting a stretch'to the thread after it leavesthe second precipitating bath. o

7. The process of -manufacturing artificia fibroin threads which comprises dissolving natural silk in phosphoric acid, adding an ethereal oil, causing the viscous solution to pass through suitably formed openings to come into contact with a liquid comprising a concentrated solution of a potassium and a sodium salt of a strong mineral acid and containing formaldehyde and an alkali metal salt of an aliphatic acid of the group consisting of hydroxy acids and acids containing the carbonyl group, passing the thread through, a second liquid comprising a concen-' trated aqueous solution of an alkali metal salt of the lower fatty acids with addition of an alkali 7 metal salt of an aliphatic acid of the group con- '7 sisting of hydroxy acids and acids containing a carbonyl group, and imparting a stretch to the thread after it leaves the second precipitating bath. 7

8. The process which comprises dissolving 1 part of natural silk wastes in 10 parts of phosphoric acid of 85 per cent strength, adding 0.04

per cent of turpentine, centrifuging the filtered solution and causing it to pass through a nozzle provided with holes of 0.08 mm. diameter in a bath containing per liter 142 grams of hydrochloric acid, 34 grams of lactic acid; 30 grams of formic acid, partly bound by potassium and partly by sodium, and grams of formaldehyde, passing the thread througha second liquid comprising a' saturated solution of ammonium 'iormate and sodium lactate, allowing the thread to run freelya long space'of air, and then imparting a stretch to the thread to form individual fibersof a titer of 1 denier.

9. As'alnew product, artificial threads con- HEINRICH FINK. ERNST ROSSNER. 

